The answer is that VPC Flow Logs do not capture traffic generated by GCP health checks. This is correct because VPC Flow Logs sample only IP traffic that traverses the VPC network, while health check probes are generated by GCP’s internal infrastructure and are not considered user-originated IP flows. On the Google Professional Cloud Network Engineer exam, this limitation is a common trap—candidates often assume all network traffic is logged, but health checks, load balancer internal communications, and Google Cloud APIs are excluded. Understanding VPC Flow Logs capabilities and limitations is critical for troubleshooting connectivity issues and tightening security posture, as the logs do capture metadata for both accepted and rejected traffic, including flows allowed by overly permissive firewall rules. A useful memory tip: if it’s a Google-managed probe, it won’t appear in your logs—think “GCP health checks are invisible to Flow Logs.”
PCNE Implementing network security Practice Question
This PCNE practice question tests your understanding of implementing network security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network engineer is troubleshooting connectivity issues with VPC Flow Logs. Which TWO statements about VPC Flow Logs are correct? (Choose TWO)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
VPC Flow Logs can be used to diagnose overly permissive firewall rules.
Option C is correct because VPC Flow Logs capture metadata about accepted and rejected traffic, including traffic that is allowed by overly permissive firewall rules. By analyzing the logs, you can identify flows that should have been blocked, revealing rules that are too broad in scope (e.g., allowing all traffic from 0.0.0.0/0). This diagnostic capability directly helps tighten security posture.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
VPC Flow Logs capture only egress traffic.
Why it's wrong here
They capture both ingress and egress traffic.
✗
VPC Flow Logs only capture traffic that is allowed by firewall rules.
Why it's wrong here
They capture both allowed and denied traffic (if logging is enabled for the rule).
✓
VPC Flow Logs can be used to diagnose overly permissive firewall rules.
Why this is correct
By analyzing logs, you can see allowed traffic and identify rules that are too broad.
Related concept
Read the scenario before looking for a memorised answer.
✗
VPC Flow Logs capture all packets for every flow in the VPC.
Why it's wrong here
Flow logs are sampled (default 1 per 10 packets) and not all flows are captured.
✓
VPC Flow Logs do not capture traffic that is generated by GCP health checks.
Why this is correct
Health check traffic is excluded from flow logs.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that VPC Flow Logs capture every packet or only allowed traffic, when in reality they sample flows and log both accepted and rejected traffic, making options B and D common traps.
Detailed technical explanation
How to think about this question
VPC Flow Logs use a flow-based sampling mechanism where each flow is defined by the 5-tuple (source IP, destination IP, source port, destination port, protocol). The logs are exported to Cloud Logging or a storage bucket, and each log entry represents a summary of the flow (e.g., total packets, bytes, and action — ACCEPT or DENY). A real-world scenario: if a firewall rule allows all traffic from 0.0.0.0/0 on port 22, flow logs will show ACCEPT entries for SSH attempts from unexpected sources, helping you identify the overly permissive rule.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Implementing network security — This question tests Implementing network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: VPC Flow Logs can be used to diagnose overly permissive firewall rules. — Option C is correct because VPC Flow Logs capture metadata about accepted and rejected traffic, including traffic that is allowed by overly permissive firewall rules. By analyzing the logs, you can identify flows that should have been blocked, revealing rules that are too broad in scope (e.g., allowing all traffic from 0.0.0.0/0). This diagnostic capability directly helps tighten security posture.
What should I do if I get this PCNE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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